In many applications, such as wireless devices and small digital equipment, an entire system can be integrated onto a single integrated circuit (IC). These ICs are commonly referred to as system-on-a-chip (SOC). SOCs usually offer several advantages over a similar design with a large number of discrete components in their reduced cost (due to a reduction in parts count), reduced power consumption, and reduced size.
Because in a SOC an entire system may be integrated onto the IC, multiple power domains may be needed to satisfy the power requirements. Each of the power domains may have different (or the same) voltage requirements. For the power domains that may have different voltage requirements, different power supplies may be used to provide the needed power.
A commonly used solution for power domains that have the same voltage requirements is to use multiple power supplies which may be designed identically to provide power to each of the power domains. This solution permits the use of multiple and relatively simple power supplies. The simple power supplies can be easier to design and be smaller, and hence easier to integrate onto the IC.
Another solution for providing a voltage to multiple power domains with the same voltage requirements is to use a single power supply that can provide the needed voltage to each of the multiple power domains. The use of a single power supply can simply the design and integration onto the IC since only a single power supply needs to be designed and integrated. Furthermore, a single power supply source may be able to offer better power supply noise immunity than multiple independent power supply sources.
One disadvantage of the prior art is that the use of multiple identical power supplies to provide the needed power to each of the power domains with the same voltage requirements is that since the power supplies are independent, there can be fluctuation in the voltages provided by the power supplies, even though the power supplies are designed to be identical.
Voltage fluctuations may lead to problems in the proper operation of clock circuits (typically seen as clock skew) and localized voltage fluctuations may lead to circuit delay and slew rate that may be outside of expected values. Voltage fluctuation may even result in the functional failure of circuitry in the integrated circuit and the integrated circuit itself.
A second disadvantage of the prior art is that the use of a single power supply to provide the needed power to each of the power domains with the same voltage requirements is that the power supply will necessarily need to be large enough to provide sufficient current. A large power supply may be hard to integrate into an IC due to its size.